The build up of heat which commonly occurs in pneumatic tires during operation can greatly accelerate deterioration of the tire. Heat has direct effects on the tire material and may also increase internal pressure to an undesirable level. In earthworking vehicles, which ride on large, costly tires, it is very often necessary to limit the rate of operation and thus the productivity of the vehicle as measured in ton miles per hour in order to reduce the effects of overheating on tires.
The adverse effects of heat on tires has been recognized by the prior art and a variety of cooling arrangements have heretofore been proposed.
A first type of cooling arrangement as proposed in the prior art is exemplified by U.S. Pat. No. 1,956,793, issued May 1, 1934 to R. Gollert, or by U.S. Pat. No. 2,948,321, issued Aug. 8, 1960 to L. C. Mote, or by U.S. Pat. No. 3,708,006, issued Jan. 2, 1973 to Calvin J. King. Cooling arrangements of this type rely on thermal conductors in the tire inflation chamber which extend from the tread region where heat is primarily generated to the rim on which the tire is mounted. The metallic rim then conducts heat away from the interior of the tire. In some cases, a quantity of liquid is provided within the tire inflation chamber to aid in heat transfer from the tire material to the thermal conductors.
In another category of tire cooling arrangements exemplified by U.S. Pat. No. 1,038,092, issued Sept. 10, 1912 to A. B. Craig, or U.S. Pat. No. 1,049,677, issued Jan. 7, 1913 also to A. B. Craig, liquid coolant contained in the inflation chamber or an inner tube is pumped to heat radiating cooling coils situated at the hub of the wheel by a pump which is driven by wheel rotation.
In still another type of prior tire cooling arrangement as described in U.S. Pat. No. 3,414,036, issued Dec. 3, 1968 to F. O. Skidmore, structures situated within the inflation chamber or formed on the inner surface of the tire itself has a configuration which increases the circulation of air or of liquid coolant or a high conductivity gas contained within the inflation chamber. Great Britain patent specification No. 1,377,489 of Douglas Bulgin discloses a variation of this type of cooling arrangement in which a volatile liquid contained within the tire is transmitted through conduits to a cooling condenser at the hub of the wheel and then returned to the inflation chamber.
Some of these prior cooling arrangements require various substantial structural changes in the tire itself and/or substantial complications of the wheel assembly as a whole. Consequently, the gains in heat elimination from the tire may possibly not be sufficient to justify the cost and complications involved. In any case it appears that prior arrangements of these types of eliminating heat from tires have not been extensively adopted by the industry. The adverse effects of heat build up on tires have continued to be a very serious problem.
The present invention is directed to overcoming one or more of the problems as set forth above.